For decades information has been stored on magnetic tape medium using tape drives. Initially the magnetic tapes were wound about large reels in similar manner as film for early film projectors. In more recent years the magnetic tape has typically been housed in a cartridge or cassette, extending internally in the cartridge from a supply reel to a take-up reel. In these cartridge applications, typically a leader tape attaches to the reel. A splicing tape then connects the leader to the magnetic tape, which in turn wraps around the reel. Cartridges may contain a supply reel only, or a supply reel and take up reel.
In some systems, the magnetic tape has longitudinal tracks recorded thereon (e.g., tracks that extend along the major length dimension of the tape). In other systems, the path of the magnetic tape is such that the tape is at least partially wrapped around a drum in a manner to transduce helical stripes or tracks on the magnetic tape. Some of the cartridges have a lid or the like which is displaced upon insertion of the cartridge into the tape drive, thereby exposing the magnetic tape to operative elements of the tape drive (e.g., tape guides, tape transport mechanisms, and transducing elements). Other cartridges are fabricated with a window or the like into which operative elements of the tape drive extend when the cartridge is loaded into the tape drive.
Some prior art techniques have been developed whereby, upon insertion into a tape drive, the tape/cartridge is identified as being of a certain type.
U.S. Pat. No. 6,385,001 shows a tape medium that has a transparent identification window segment. The identification window segment has a length that is chosen to provide a predetermined medium or cartridge signature when the medium is transported at a selected linear velocity.
For example, techniques are known for automatic identification of a DAT (digital audio tape) and DDS (digital data storage) tape.
DAT and DDS tape cartridges have the same form factor. DDS tape medium differs from DAT audio tape medium primarily in terms of the quality of the magnetic coating on the tape for increased reliability of the data storage on the tape medium. A DAT audio tape cassette physically fits into a DDS drive, and data can be written to and read from it, but it is likely that the user will experience a significant level of unreliability and loss of data.
GB2266402A discloses a tape medium having a transparent splice or splicing tape that has at least one opaque stripe located on it over the leader tape for automatic recognition of DDS tape, thus distinguishing DDS cartridges from identically sized DAT cartridges. The tape drive has circuitry for finding the junction of the data storage portion of the tape medium and the leader tape by monitoring the output signal of an optical sensor. When toggling of the sensor output signal is detected this indicates that the opaque stripe is present and that the cassette is a DDS type. The absence of toggling indicates that the cassette is not a DDS type, in which case a write-protected mechanism of the tape drive is activated to prevent writing of data to the tape medium and thus the possibility of loss of that data.
The standard ECMA-288, June 1999, that is available from http://www.ecma.ch shows a corresponding medium recognition system (MRS) in its chapter 9.16. In accordance with this standard a pattern of alternating clear and opaque stripes shall exist along the entire length of the splicing tape at the physical beginning of the tape, i.e. where the leader tape is joined to the magnetic tape. The light transmittance through the combination of the opaque stripes and the leader tape shall be 5% max. The light transmittance through the combination of the clear stripes and leader tape shall be 60% minimum. Annex B of the standard ECMA-288 shows the general principle of measuring equipment and a measuring method for measuring the light transmittance of the tape.
In addition to the differentiation between DDS tape medium and DAT tape medium the various format generations of DDS tape medium need to be detected automatically. The problem of distinguishing former generations in DDS cartridges is typically handled by detecting a pattern of four holes, called recognition holes, in the cartridge shell. Annex K of the ECMA-288 standard defines recognition hole patterns and the related DDS format generations 1 to 5 as well as the DAT format (IEC1119-1) represented by the respective recognition hole patterns.
A disadvantage of the recognition holes is that they provide limited information carrying capacity so that only the tape medium format can be encoded, and also that the mechanical sensing of the recognition hole patterns is relatively unreliable and can be subject to mechanical failure.